Understanding Air Purifiers

May 27, 2009

Purchasing an air purifier can be confusing, and you do get an awful lot of information thrown at you when you visit the different manufacturing websites, don't you? How can you tell what's what, and why do we need air filters anyway? And how do air purifiers work? Is the air really that bad? Haven't we been breathing the same air for thousands of years?
Yes and no. First of all, we've been breathing the same air for thousands of years, but we live in a symbiotic relationship with the plants around us – that is, we rely on each other to survive. We breathe oxygen to live, and give off carbon dioxide. Plants exchange carbon dioxide for oxygen, effectively "exchanging" the air in a healthy relationship with us. This makes plants the first primitive air purifiers on earth, and explains why scientists are so concerned about the ecological balance on earth and the need for the survival of rain forests and plants – they ensure our own survival as well by preserving oxygen in our atmosphere.
Nature cleans the air in other ways as well – ozone (positively charged oxygen molecules) is generated by waterfalls and thunderstorms. Ozone also cleans impurities and particulates from the air naturally.

The Industrial Revolution and Air Quality

The industrial revolution made great strides in everything but air quality. In fact, pollution such as emissions from automobiles, smog and pollution from everyday chemicals like cleaning fluids, carpeting and paints enter the air every day. In industrial settings, air purifiers clean the air before it is released into the atmosphere in order to meet government requirements.

Today's homes are also more energy efficient and cost effective, but to get there they have become much more "closed in." When they are this sealed up, indoor pollutants are shut in so that today's homes are actually two to five times more polluted than outdoor levels! Obviously, air purifiers are essential to improving indoor air quality to combat the effects of this stale, recirculated air.

Beginning in the 1980's, medical practitioners began to take note of the direct link between poor air indoor air quality and the increased incidence of conditions such as asthma, allergies and recurring colds and upper respiratory infections. The development of a variety of improved, scaled-down air filtration systems for in-home use soon emerged.

How the Main Types of Air Purifiers Work

One of the most commonly used type of air purifier is also one of the first developed, and is used in most hospitals and clean rooms. This is the HEPA filter.

HEPA Filters

During the Manhattan Project in the 1940's, the Arthur D. Little firm developed the first HEPA filters in order to filter out very small particles that had become contaminated by nuclear radiation in atomic bomb testing areas. It was during this initial development that the HEPA standards were set at 0.3 microns, which could effectively capture condensed radioactive iodine.

The filters at that time were called "absolute filters," and not called HEPA (High Efficiency Particulate Air) until the filters were marketed in the 1950's. Today these filters are used by hospitals, surgical wards, biopharmaceutical research labs, micro circuitry labs, and the aerospace industry for their exceptional ability to control dust and particulates.

HEPAs remove 99.97% of particles of 0.3 microns or larger. For even more intense filtration, there is an ULPA, or Ultra-HEPA filter, which filters out 99.99% of contaminants pass through the filter.

Obviously, something has to draw the air through the filter, and with HEPA filters this is a motorized fan. This can make them noisy, which makes them an annoyance to some people. A HEPA filter will need to be replaced every 12-18 months, depending upon how it is used and the interior environment of your home. For instance, if you have pets, especially cats or dogs that shed a lot, you may need to change it more frequently because of the dander. If there are smokers in the house you will also need to change your air filter more frequently to ensure proper filtration.

However, for overall performance, nothing filters out or eliminates more particulates than a HEPA filter, so it is a matter of balancing cost, sound preference and convenience against your relative needs when choosing the right model of air cleaner for your home.

Ozone Air Purifiers

Ozone is created in nature by everything from waterfalls to thunderstorms, and is responsible for that fresh, clear smell after a heavy rain or storm has passed. It's nature's way of cleaning the air. Ozone air purifiers essentially do the same thing indoors by artificially mimicking the natural process that creates ozone.

Ozone molecules exist in the air all around us, and will react with any particles they come into contact with, but are very unstable and tend to exist in small quantities for short periods of time.

Ozone air purifiers work by using electricity to generate more ozone molecules, which have one more oxygen (O3) than we normally have in the air (O2) around us. Since ozone is highly unstable, one of the oxygen atoms is always inclined to break away and find another molecule to bond to. This process causes a chemical reaction which destroys odors and germs in the air and then converts what is left of the molecules into harmless oxygen and CO2.

There is some confusion between ozone air cleaners and ionic air cleaners, but there are some differences. With an ozone air purifier, the ozone that is released into the air will be unstable and cause a reaction that will alter and destroy certain germs, viruses, bacteria and molds. It does not, however, have a collection plate where dirt or grime collects.

Ionic Air Cleaners

An ionic air cleaner also uses electrical charges to alter oxygen atoms in the air, like an ozone air cleaner. But unlike an ozone cleaner, an ionic air cleaner will rid the air your breathe of dust and pollen as well.

Ionic air cleaners negatively charge the air particles in a room, which will cause a magnetic attraction to occur. The positively charged particles in the air, such as dust, pollen and pet dander, will naturally be attracted to these and they will "cling" to each other, creating a sort of magnetic bond. Particles that form into bonds like this become too heavy to remain suspended in the air and fall to the ground, where you will no longer be able to breathe them into your system.

Vacuuming and regular dusting can get rid of these particles. In today's ionic cleaners, there are also fans that move the room air over negatively charged metal collection plates that the positively charged particulates will stick to. These can be regularly cleaned by simply wiping them with a soft cloth.

Electrostatic Precipitators

The original electrostatic precipitators were huge monsters used to control pollution emissions from industrial plants. The waste by-products of a plant were sent through large chambers that were charged by electrodes that acted as enormous collection plates to attract the oppositely charged waste products (such as dust, lead, sulfur, fly ash and other hazardous chemicals) from the materials passing through, filtering out all harmful materials. Periodically, the precipitators would be "tapped" so that these materials could be dumped from the chambers into disposal units.
Home electrostatic precipitators also work on the theory of using a negative charge and a positive charge to collect and retain particulates, however, the charge takes place within the air purifier itself rather than in huge chambers, and the dust and particulates are captured on metal filters that can be removed and cleaned or replaced, getting rid of the need for a separate collection chamber for the particulates.

Electrostatic Filters

With electrostatic filters, a small static charge is created that attracts airborne particles as they go through a filter, capturing even those particulates which are too small too be captured by the relatively loose weave of the filter itself. Because of the looser weave, the air flow in an electrostatic filter is very good, but the filtration is very effective because of the electrostatic charge.

These filters do have to be carefully maintained and cleaned at least monthly, and should be replaced every year for peak effectiveness. As the filters do become dirtier, the air flow will become less efficient.

Finally, there are systems that combine two or more types of air purification system. While these are usually more expensive, they can be worth the price if you are looking for the best possible combination of features. For instance, an air purifier that will kill viruses and bacteria like an ozone air purifier, but will also effectively filter out dust and dander with a HEPA filter.

About the Author
Lori Wilkerson is a full-time freelance writer. Right now she knows a little bit about almost everything and a lot about electrical air purifiers, HEPA air cleaners, and whole house air purifiers. Her own home is polluted with several hundred books, pet dander and roving bands of teenagers.